NAND flash memory has a characteristic in that, when it is read-accessed intensely, data corruption (read disturb) occurs in pages around a page to be accessed. Such a characteristic is prominent as the flash memory circuit becomes smaller and smaller.
As a way to cope with the occurrence of read disturb, there is known a method for detecting a page in which read disturb has occurred and then moving data of this page to another page.
For example, the number of accesses to a block of a flash memory is counted. When the block is read a certain number of times or more, read access is made to all pages of the block, and then whether read disturb has actually occurred in the pages or not is checked (see Patent Literature 1 and Patent Literature 2, for example).